Process of making leather-rubber material



Patented Mar. 29, 1938 2,112,517

'UNITED STATES PATENT OFFICE 2,112,517 rnocsss or MAKING LEATHER-RUBBERMATERIAL 4 Donald E. Cable, Rutherford, N. J., assignor, by mesneassignments, to United States Rubber Company, New York, N. Y., acorporation of New Jersey No Drawing. Application October 10, 1933,Serial No. 692,991

3 Claims- (Cl. 9221) This invention relates to a process of making thepresent method a dispersion of negatively leather-rubber material andmore particularly charged rubber pa ti es s P e y dded to toleather-rubber sheet material made from aquean aqueous leather fibresuspension the fibres of ous suspensions of leather fibres and aqueousdiswhich a P vely charged n a u p d Ii persions of rubber, such asrubber latex. in an aqueous medi m h vin 41 P m ou Leather-rubber sh etmat ial i c m only 4.2 to 6.5. The resulting product consists of a madefrom leather scrap ord t r l athe h vporous sheet or mass of feltedleather fibres with ings by beating the same until th fibres re in latexrubber intimately and uniformly distributed the desired suspended formin water. The rethroughout t e mass and aflixed to the indi- 0 suitingsuspension of leather fibres is then com- Viduel fi The P s are e pec ycharl0 monly made alkaline by the addition of alkaline a ed by theabsence of any visible lumps or salts or free bases, and thereafter analkali-preclots of u a d th r f ha e a unusua ly served aqueousdispersion of rubber is added to fi grained s u u nd pl as n app aran e.the mixture. A coagulant, for example aluminum In their resistance o P pCreeklng d W sulphate, is then added to precipitate the rubber ufl s,the p du ts mpar fav ra y with 5 in the mixture, which is then filteredon an ordihigh-grade leethery are Particularly Sultnary paper-makingscreen, sh t may t able for the manufacture of such articles'as inbemanufactured from the filtered material by Soles, upholstery, u e, andthe like. drying, pressing and finishing as desired. Previ- AS 11Specific illustration o carrying out the m ous attempts to preparerubber-leather products Present invention, but Without t on to limit 2t)containing as much as 33% of rubber by the the invention except asrequired by the prior art, coagulation of rubber from latex upon leatherthe fellowihg Present p ed et od Of carfibres suspended i a aqueous lhave rying out the invention is described in detail. sulted in productscontaining numerous visible Water-leached Chrome leather ap, S ing g5clots or lumps of rubber relatively-free of fibres, dust mixtures of theSame are l d wit due to the coagulation of the rubber particles Water t0e consistency of 0 P ts Of before they could become attached to thefibres. at p 100 parts of at and at n/t Such clots of rubber give to theproduct a coarse fem a uniform SUSDeDSiOII 0f t e dividual grainedstructure and unsightly appearance. In lea-the! fibres Which y have a Dfro about the manufacture of rubber-leather productsby t0 The Suspendedmineral tanned fibres 30 methods comprising the admixture of aqueous areknown to carry positive e ct charges and leather fibre suspensions andaqueous dispertherefore have an aflinity for negatively charged sions ofrubber and the coagulation of the rubparticles Such as latex globules, dare capa e her in the resulting mixtures, it has not been of dsorbingrubber pa t p to about 20 0 previously recognized that substantialswelling of the weight o the fi The affinity 01 35 of the leather fibreoccurs in the range of OH the leather fi e for e latex obules may be ionconcentrations on the alkaline side of neuincreased the addition of arelatively small trality and is especially pronounced above a pH amountof dior tri-valent cation material, such of about 7.8, while a minimumof swelling 00- as zinc chloride, aluminum su phat alum, r ours in therange of pH values from about 42 the like, Preferably added some littletime Prior 40 to about 7.8. I have now discovered that greatto theaddition of the letexlin Order t0 P mi 1y improved rubber-leatherproducts may be obadsorption o id s by e fibres- F examtained by suchprocesses wherein the pH of the o t n par f hy at d aluminum su p perfibrous suspension is maintained throughout the 100 Parts Of Suspendedleather fibres y he 4:; process at such values that a minimum of swelledto the s p n ion to in r he d orbin 45 ing of the fibre is insured.capacity of the fibres for the rubber particles The present inventionrelates to a process of to or more of the weight of the fibres. Themaking rubber-leather products from suspensions pH of the thus treatedfibre suspension remains of leather fibre and rubber wherein the pH ofaround 5.0 to 6.2. The aluminum sulphate added the aqueous vehicle ismaintained at values from also insures that the pH of the fibresuspension 60 about 4.2 to 7.8, and preferably at values not will remainbelow 7.8 during the subsequent adhigher than 7.0, throughout the stepsof beating dition'of an alkaline latex. The mixture is prefthe fibresand all the subsequent operations, parerably allowed to stand for atleast one-half ticularly that of incorporating the aqueous dishour, andthe latex may then be added in such persion of rubber with the fibresuspension. .By amount as to provide up to about one part of 55 rubberto two parts of fibre (on a dry basis). By such method the precipitationof the rubber directly onto the fibres begins immediately upon theaddition of the latex to the mildly acidic fibre suspension, wherebysubstantially all of the rubber globules become firmly and uniformlyaffixed to the individual leather fibres, and there is formed afree-flowing suspension of individually rubberized fibres which iscapable of being subjected to the further paper-making operations suchas pumping, recirculation, and screening. The pH of the fibre suspensionprior to the addition of the latex is preferably kept between about 4.2and 6.5. By the maintenance of the pH of the system continuously between4.2 and 7.8, and preferably between 4.2 and 7.0, during the subsequentaddition of the latex, a slow, controlled and complete coagulation ordeposition of the rubber globules from the dispersion onto the leatherfibres takes place. This deposition on the fibres takes place chieflydue to the attraction between the negative charges of the latex globulesand the positive charges on the chrome leather fibre, the latterpreferably being augmented by the addition of a dior trivalent cationmaterial such as aluminum sulphate, as above described. In place of theusual alkaline latex I may employ an acid latex having a pH of above 4.5and wherein the rubber globules are negatively charged. Such acid latexmay be prepared by well known methods such as are disclosed, forexample, in the patents to McGavack and Shive Nos. 1,699,368 and1,699,369 granted January 15, 1929. A normal latex of which'the ammoniacontent has been substantially reduced by air-blowing, or treatment withformaldehyde or silica gel, or by other methods, may also be used in theprocess to good advantage. Another method of insuring the maintenance ofthe pH between 4.2 and 7.8 is by the addition of an acid material in anamount equivalent to the known amount of ammonium hydroxide or otherbase in the added alkaline latex. The system, after the addition of thedesired amount of latex, should preferably contain up to about 33%rubber (on the dry combined solids) and have a pH above 5.0 and below7.0, preferably around 6.5. If the rubber particles have not'beencompletely coagulated, a small amount of acidreacting material such asaluminum sulphate, acetic acid or the like may if desired be added tocompletely clear the serum and aid in filtering. The water suspendedfibres with rubber deposited on them may then be fiat screened, ifdesired, and are then filtered in the ordinary manner, using paper,paper board, wet machines or other sheet forming equipment. The feltedor interlocking fibre structure is then pressed, dried, and finished asdesired.

The leather fibre is preferably mineral tanned but vegetable tannedfibres may be used alone or mixed with the mineral tanned fibres.Vegetable tanned fibres, however, require the adsorption of largeramounts of dior tri-valent cations to provide a suspension having thedesired characteristics. The aqueous i p r ion. of

rubber added to the suspension of leather fibres may take the form of anatural (normal or concentrated) latex or an artificial dispersion ofrubber or rubber-like material. Unvulcanized or vulcanized latex, forexample, may be used, and if unvulcanized, the rubber deposit on thefibres may be subsequently vulcanized, or not, as desired. Themanufacture of a simple leatherrubber combination has been describedabove, but it is obvious other constituents, such as cellulose fibre(from cotton or chemical wood pulp), organic or mineral coloring matter,zinc oxide,

rubber curatives, accelerators and anti-oxidants,

may be incorporated with the fibre and rubber materials.

With the above detailed disclosure of the invention, it is evident thatnumerous modifications will suggest themselves to those skilled in theart, and it is not desired to limit the invention otherwise than as setforth in the appended claims.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. The process of making leather-rubber material comprising forming anaqueous suspension of leather fibres, mixing therewith a water-solublesalt of a polyvalent metal and thereafter allowing sufilcient time forsubstantial adsorption of multi-valent cations by the fibres to takeplace while maintaining the pH of the thus treated suspension at fromabout 4.2 to 6.5, subsequently mixing with' such suspension an aqueousdispersion of rubber in which the dispersed rubber particles arenegatively charged while maintaining the pH of the resulting mixturebetween 4.2 and 7.8 whereby the rubber becomes firmlyand uniformlyattached to the fibres, abstracting liquid, drying and finishing.

2. The process of making leather-rubber material comprising forming anaqueous suspension of leather fibres, mixing therewith a water-solublesalt of a polyvalent metal to effect substantial adsorption ofmulti-valent cations by the fibres while maintaining the suspension at apH of from about 4,2 to 6.5, thereafter mixing therewith an aqueousdispersion of rubber in which the dispersed rubber particles arenegatively charged while maintaining the pH of the resulting mixturebetween 4.2 and 7.8, then adding asmall amount of acid reacting materialto completely clear the serum and coagulate any still uncoagulatedrubber particles, abstracting liquid, drying and finishing.

3. In the process of making leather-rubber material, the step of mixingan aqueous dispersion of negatively charged rubber particles with anaqueous suspension of leather fibers having a pH value of from about 4.2to about 6.5 and having adsorbed on the fiber sufflcient polyvalentcations to efi'ect the coagulation and deposition on the fibers of20-50% of rubber, referred to the dry fiber weight, upon admixture ofsaid rubmixture between 4.2 and 7.8.

DONALD E. CABLE.

